Topic 2 - Sub-aerial processes Flashcards
1
Q
What is weathering?
A
- The breakdown disintegration of rock in situ (without rock movement), at, or close to ground surface
2
Q
What is freeze-thaw?
A
- Occurs when water enters a crack or joint in the rock when it rains and then freezes in cold weather
- When water freezes, it expands in volume by 10% - this expansion exerts pressure on the rock, which forces the crack to widen
- With repeated freezing and thawing, fragments of rock break away and collect at the base of the cliff as scree then used as tools by the sea for marine erosion
3
Q
What is salt crystalisation?
A
- When salt water evaporates, it leaves salt crystals behind - these can grow over time and exert stresses in the rock, causing it to break up
- Salt can also corrode rock, particularly if it contains traces of iron
4
Q
What is wetting and drying?
A
- Rocks that are rich in clay expand when they get wet and contract as they dry-this can cause them to crack and break upon as they lose coherence and structure
5
Q
What is biological weathering?
A
- The break-up of organic activity
- Thin plant roots grow into small cracks in a cliff face-these cracks widen as the roots grow, which breaks up the rock
- Water running through decaying vegetation becomes acidic, which leads to increased chemical weathering
- Birds and animals dig burrows into cliffs, marine organisms are also capable of burrowing into rocks or of secreting acids
6
Q
What is chemical weathering?
A
- Involves a chemical reaction where salts may be dissolved or a clay-like deposit may result which is then easily eroded
- Carbonation
- Oxidation
- Solution
7
Q
What is carbonation?
A
- Rainwater absorbs carbon dioxide from the air to form a weak carbonic acid-this reacts with calcium carbonate in rocks, to form calcium bicarbonate, which is easily dissolved
- The cooler the temperature of the rainwater, the more carbon dioxide is absorbed
8
Q
What is oxidation?
A
- Rocks disintegrate when oxygen (dissolved in water) reacts with some rock minerals, forming oxides
9
Q
What is solution?
A
- The dissolving of rock minerals, such as halite (rock salt)
10
Q
What is mass movement?
A
- The downfall movement of material under the influence of gravity
- Soil creep
- Mudflows
- Soilfluction
- Runoff
- Landslides
- Rockfall
- Landslip/rotational slip/slumping
11
Q
What is physical weathering?
A
- Freeze-thaw
- Salt crystalisation
- Wetting and drying
12
Q
What is soil creep?
A
- An extremely slow form of movement of individual soil particles downhill
- Caused by particles being displaced due to wetting and drying cycles, followed by downward movement from gravity
- Cannot be seen in operation, but can see its impacts
- Shallow terracettes
- Bending of tree trunks
- Poles tilted
13
Q
What are mudflows?
A
- Involves earth and mud flowing downhill, usually over unconsolidated or weak bedrock-often after heavy rainfall
- Usually on a slope over 10 degrees
- Water can’t percolate, therefore saturates top layer
- Water gets trapped within the rock, increasing pore water pressure, which forces more particles apart and leads to slope failure
- Often sudden and fast-flowing so can represent a significant natural hazard
14
Q
What is solifluction?
A
- Similar to soil creep but specific to cold environments where temperatures fluctuate around freezing
- In the summer, the surface layer of the soil thaws out and becomes extremely saturated as it sits on top of impermeable permafrost
- Gentle slopes, smaller than 10 degrees
- Known as active layer, this sodden soil with its blanket of vegetation slowly moved downhill by a combination of relief and flow-this results in unique landforms known as solifluction lobes
15
Q
What is runoff?
A
- When overland flow occurs down a slope or cliff face, small particles are moved downslope towards the coastline
- When heavy rainfall washes material from the surface of a cliff face over the edge and down onto the shore
